<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .container{
            height: 40px;
        }
        /* pc min-width:992px */
        @media (min-width:992px){
            .container{
                width: 1170px;
                background: red;
            }      
        }
        /* ipad 大于768px 小于992px */
        @media (min-width:768px) and (max-width:992px){
            .container{
                width: 750px;
                background: blue;
            }
        }
        /* iphone 小于768px */
        @media (max-width:768px){
            .container{
                width: 375px;
                background: green;
            }
        }
    </style>
</head>
<body>
    <!-- pc 1170px  bg red
         ipad 750px bg blue
         iphone 375px bg green
         @media screen
    -->
    <div class="container">
       
    </div>
</body>
</html>